Disubstituted ureas are usefully used as starting materials or intermediates of agrichemicals, herbicides, insecticides and carbamates and various methods for their preparation are being studied.
The existing method of preparing urea by reacting an amine with phosgene is disadvantageous in that the highly toxic and corrosive phosgene is used and a large amount of the pollutant HCl is produced as byproduct. Accordingly, methods for preparing urea without using the harmful phosgene have been studied in the US, Japan and Europe.
U.S. Pat. No. 2,877,268 discloses a method for preparing urea by reacting an amine with carbonyl sulfide (COS) in the absence of a catalyst, and the literature “J. Org. Chem. (R. A. Franz, 26, p. 3309, 1961)” discloses a method for preparing urea by reacting an amine with carbon monoxide (CO) and sulfur (S) using a tertiary amine as a catalyst. However, these methods are problematic in that byproducts difficult to handle such as H2S are produced because sulfur is used.
Japanese Patent Publication No. S62-59253 discloses a method for preparing urea from a nitro compound using a catalyst such as rhodium, ruthenium, etc. Although this method allows preparation of urea with relatively high conversion rate and selectivity, the expensive noble metal catalyst may be easily decomposed because of high reaction temperature and pressure.
European Patent No. 0 319 111 discloses a method for preparing urea from a mixture of an amine and nitrobenzene using a noble metal catalyst palladium with a salt of copper, iron, manganese, vanadium, chromium, etc. added to maintain the activity of the palladium catalyst. As described in Example 1 of the EP 0 319 111, this method is problematic in that the maximum yield of urea is low as 73% (turnover frequency, i.e., the number of moles of urea produced per unit time, per a mole of catalyst <4) when reacted for 20 hours under the condition of 140° C. and 50 atm.
A method for synthesizing aliphatic urea by carbonylation of an amine in the presence of a selenium catalyst is described in “Chemistry Letters (Koyoshi Kondo, p. 373, 1972)”. This method is problematic in that a large amount of the catalyst is spent since the selenium is used in an equimolar amount with respect to the starting material amine and that the reaction hardly proceeds if an aromatic amine is used as the starting material.
U.S. Pat. No. 4,052,454 discloses a method for synthesizing urea by reacting a nitro compound with water and carbon monoxide in the presence of a selenium metal catalyst. This method is economically unfavorable since, as described in Example 1 of the U.S. Pat. No. 4,052,454, nitrobenzene conversion rate and urea yield are only 66.3% and 33.8% (turnover frequency, i.e., the number of moles of urea produced per unit time, per a mole of catalyst <2) when reacted for 1 hour under the condition of 150° C. and 53 atm, with a molar ratio of the catalyst to the starting material nitrobenzene of about ⅛.
As described above, the existing methods for preparing substituted urea are inappropriate for preparation of the substituted urea in industrial scale because of byproduct formation, reaction condition with high temperature and pressure, and low yield, and are problematic in that it is difficult to prepare urea in high yield when a less reactive aromatic amine is used as a starting material in spite of the reaction condition with high temperature and pressure. And, the method for preparing urea using selenium as a catalyst also has a problem because of the characteristic unpleasant odor of selenium after the reaction under the condition with high temperature and pressure.
Hydroxyalkyl carbamates are synthetic intermediate useful in various fields, including drug synthesis and agrichemical production, and as precursors of polyurethane.
As an existing method for preparing a hydroxyalkyl carbamate, Korean Patent No. 10-0050365 discloses preparation of 2-hydroxypropyl carbamate by reacting propylene carbonate with a primary or secondary aliphatic amine.
Also, U.S. Pat. No. 4,268,684 (Arthur E. Gurgiolo) discloses a method for preparing an aromatic carbamate by reacting an aromatic amine, e.g., aniline, with dimethyl carbonate, and U.S. Pat. No. 4,550,188 discloses a catalyst for reacting an aromatic amine with an organic carbonate, including a mercury salt and iodine. However, there are problems of the toxicity of mercury and low performance of the catalyst. Also, the aromatic polyurethane derived from the aromatic carbamate synthesized from the aromatic amine has unsatisfactory physical and chemical properties as compared to aliphatic polyurethane due to yellowing.
Meanwhile, Korean Patent Publication No. 1991-0009114 relates to a novel hydroxyalkyl carbamate having one or more secondary amine groups in the molecule and a method for preparing same, and describes preparation of a hydroxyalkyl carbamate from a polyfunctional amine having at least one primary amine group and at least one hindered secondary amine group, wherein the primary amine group(s) react(s) selectively with a cyclic carbonate and the secondary amine group(s) remain(s) unreacted.
Korean Patent No. 10-0576404 relates to a β-hydroxyalkyl carbamate-modified resin for pigment dispersion and a cationic electrodeposition paint composition containing same, and describes preparation of a β-hydroxyalkyl carbamate from reaction of a cyclic carbonate with a polyepoxide-amine resin.
U.S. Pat. No. 6,165,338 relates to a cathodic electrodeposition coating composition and describes preparation of a hydroxyalkyl carbamate from reaction of a primary or secondary amine or diamine with a cyclic carbonate such as ethylene carbonate.